Thanks - but am not looking at trying to give a USB solution - just pure SPI (already have UART and I2C options). Had a quick look at the docs on that site and cant see anything obvious about the SPI port.
My main concern is to make connectivity easy. ie look at one mcu board and the uart may be 1x3 headers: gnd,tx,rx but look at another and it may be gnd,rx,tx. So you need to make up yet another cable.
The main thing I dislike about the ISP 2x3 pin arrangement is that most people dont have a connector like that in their spares box. So I was hoping a 1x4 arrangement might exist.